Help with physics problem
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Help with physics problem

[From: ] [author: ] [Date: 12-05-29] [Hit: ]
If the diesel engine travelling at 5 km/h hits a freight car that is initially at rest, how fast do they both move after they have coupled together?Thanks!-Conservation of Momentum applies.Let the mass of the freight car be M kg.= 20M kg.......
If anyone could explain how to solve this problem, I would greatly appreciate it.

A railroad diesel engine weighs four times as much as a freight car. If the diesel engine travelling at 5 km/h hits a freight car that is initially at rest, how fast do they both move after they have coupled together?

Thanks!

-
Conservation of Momentum applies.

Let the mass of the freight car be M kg.

Hence the mass of the engine = 4M kg

Momentum of the engine on its own = 5 * 4M
= 20M kg.km/h

Momentum of the two together
= 20M (momentum is conserved)
but the mass is now 5M

Speed * Mass = 20M

Speed = 20m / 5M = 4 km/h
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